Hybrid Cord and Use Thereof

ABSTRACT

A hybrid cord comprises (i) a first yarn, without initial S or Z twist, of continuous polymeric filaments forming the core of the cord, the yarn being a non-bulked yarn, (ii) a second yarn, without initial S or Z twist, of continuous polymeric filaments, the second yarn being a bulked yarn that is wrapped around the first yarn, wherein (a) the second yarn is wrapped around the first yarn at an angle of from 5 to 40 degrees, (b) the second yarn has a length that is from 4 to 35 percent longer than that of the first yarn, and (c) the hybrid cord is unbalanced and has an S or Z twist.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention pertains to a hybrid cord that is suitable for use as a reinforcing material in a hose.

2. Description of Related Art

Different types of materials, for example one having a higher modulus and one having a lower modulus, are often used together in hybrid cords for applications such as reinforcement in a high pressure hose or in a tire.

There remains a need for hybrid cords produced on conventional textile machines that will provide enhanced reinforcement against burst pressure in a high performance hose. In this respect, it is desirable to maximize, in the hybrid cord, the synergistic benefit of the yarn properties such as modulus and elongation at break of the component yarns that form the cord.

U.S. Pat. No. 7,155,891 to Bader describes a substantially torqueless composite dual core-spun yarn that has a substantially inelastic central hard core covered with a dual-spun fiber covering. The central hard core has an elongation at break less than 50% and a Z or S twist, and the fiber covering comprises fibers twisted on the core with an S or Z twist opposite to that of the core. The opposite twists of the core and of the covering exert opposite and substantially equal torques. This yarn is produced by introducing two slivers forming the covering and a central core in a spinning triangle. The core is fed overtwisted S or Z and the slivers have an opposite Z or S twist corresponding to about 30% to 70% of the twist of the fed overtwisted core that detwists during spinning. The inelastic core is fed at controlled speed to compensate for the angle of feed and to compensate for detwisting, and is guided into the spinning triangle by a guide groove in a feed roller.

United States Patent application publication number 2014/238524 to Love et al. discloses a hybrid cord formed from a plurality of component plies wherein at least one of the plies has a length that is from 1 to 50 percent longer than the other plies and a method of providing a cord with predetermined twist and component ply lengths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a representation of a hybrid cord of this invention.

FIG. 2 is a schematic of the method for forming the hybrid cord

FIGS. 3-6 pertain to the described examples.

FIGS. 7-8 are force vs. strain curves of the examples.

SUMMARY OF THE INVENTION

This invention pertains to a hybrid cord comprising

(i) a first yarn, without initial S or Z twist, of continuous polymeric filaments forming the core of the cord, the yarn having a tenacity of 2.2-16.6 g/dtex, a modulus of from 1 to 20 GPa and an elongation at break of greater than 8%, the yarn being a non-bulked yarn, (ii) a second yarn, without initial S or Z twist, of continuous polymeric filaments, the yarn having a tenacity of greater than 16.6 g/dtex, a modulus of greater than 20 GPa and an elongation at break of no greater than 8%, the second yarn being a bulked yarn that is wrapped around the first yarn, wherein, (a) the second yarn is wrapped around the first yarn at an angle of from 5 to 40 degrees, (b) the second yarn has a length that is from 4 to 35 percent longer than that of the first yarn, and (c) the hybrid cord is unbalanced and has an S or Z twist.

DETAILED DESCRIPTION OF THE INVENTION

By hybrid cord we mean a fibrous cord comprising at least two components that are combined together, usually by twisting. This is also known as a plied cord. Each component may be a single filament or, preferably, a yarn comprising a plurality of filaments. The fibers or filaments are continuous. By continuous is meant that they are of indefinite or extreme length having a very high length to thickness or high length to width ratio. Continuous filaments are desirable for this invention as unlike short or long staple fiber spun yarns, continuous filaments do not slip and pull apart while under tension in a knitting machine. This pulling apart is often referred to as linting, a well-known term in the textile art.

A second disadvantage of short or long staple fiber spun yarns is that, when fabricated into a fabric or knit for a hose, they can extend under continuous loads because the individual fibers can slip one versus the others thus increasing significantly the diameter of the hose.

In the context of this application, a bulked or textured yarn is a yarn formed from continuous filaments that do not lie parallel to each other and create a fluffy or bulky appearance. There are air gaps between some of the filaments in a bulked yarn. A non-bulked yarn is a yarn where the filaments lie essentially parallel to each other and have no or minimal air gaps between adjacent filaments.

In a preferred embodiment, the hybrid cord comprises a first yarn, without initial S or Z twist, of continuous polymeric filaments forming the core of the cord, the yarn having a tenacity of 2.2-16.6 g/dtex (2 to 15 g/denier), a modulus of from 1 to 20 GPa and an elongation at break of greater than 8%, the yarn being a non-bulked yarn and a second yarn, without initial S or Z twist, of continuous polymeric filaments, the yarn having a tenacity of greater than 16.6 g/dtex (15 g/denier), a modulus of greater than 20 GPa and an elongation at break no greater than 8%, the second yarn being a bulked yarn that is wrapped around the first yarn. S and Z twist terms are well known in the art. By “without initial S or Z twist” is meant that the first and second yarns are untwisted as component yarns until combined into a hybrid cord and if the hybrid cord was disassembled back into first and second component yarns, these two component yarns would be untwisted.

By yarn is meant a continuous strand of textile fibers or filaments in a form suitable for weaving, knitting or otherwise intertwining to form a cord or textile fabric. FIG. 1 shows generally at 10, a portion of a hybrid cord comprising a first yarn 11 that is a non-bulked yarn forming the core of the cord 10 and a second yarn 12 comprising a plurality of filaments that is a bulked yarn that is wrapped around the first yarn 11 at a wrap angle of from 5 to 40 degrees. Preferably the wrap angle is from 10 to 30 degrees. The first yarn comprises a plurality of filaments. Although yarn 11 has no S or Z twist, the individual filaments comprising the yarn are twisted, either in an S or Z direction These individual filaments also lie parallel to each other within the yarn. FIG. 1 does not show the twist in the individual filaments. To demonstrate a plurality of filaments in yarn 11, FIG. 1 shows the individual filaments as spaced apart whereas in reality, adjacent filaments contact each other. In some embodiments, the second yarn 12 has a length that is from 4 to 35 percent longer than that of the first yarn 11. In other embodiments, the second yarn 12 has a length that is from 6 to 20 percent longer than that of the first yarn 11. In yet other embodiments, the second yarn 12 has a length that is from 6 to 15 percent longer than that of the first yarn 11 or even 6 to 8 percent longer. The elongation at break of the first yarn 11 is greater than the elongation at break of the second yarn 12, In some embodiments, the second yarn 12 is a singles yarn and covers from 70 to 99 percent of the surface area of the first yarn 11, A singles yarn is a well-known term of art and applies to a yarn that has not been combined (plied) with another yarn in such a way that it can become separate again.

The initially untwisted first and second yarns are assembled into the hybrid cord 10, such that the hybrid cord is unbalanced and has an S or Z twist. By “unbalanced:” is meant that the twist of the hybrid cord is not offset by the counter twist of the component yarns as the component yarns have no initial twist.

The amount of differential length between the first and second yarns is selected to suit specific performance requirements. In some embodiments, the first yarn has a linear density of from 111 to 11111 dtex (100 to 10000 denier) or from 222 to 6666 dtex (200 to 6000 denier) or even from 888 to 4444 dtex (800 to 4000 denier). In some embodiments, the second yarn has a linear density of 111 to 11111 dtex (100 to 10000 denier) or from 222 to 6666 dtex (200 to 6000 denier) or even from 888 to 4444 dtex (800 to 4000 denier). In some embodiments, the hybrid cord has a linear density of from 222 to 11111 dtex (200 to 10000 denier) or from 555 to 5555 dtex (500 to 5000 denier) or even from 1111 to 4444 dtex (1000 to 4000 denier).

By polymer, is meant a high molecular weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit. Some polymers are made from two or more dissimilar monomers and are often referred to as copolymers. Preferably, the polymer of the first and second yarns is polyester, aliphatic polyamide, aromatic polyamide, aromatic co-polyamide, polyimid, polyamide-imide, polyazole, or a bio-based polymer. Another suitable polymer is an aromatic copolymer derived from the copolymerization of para-phenylenediamine, 5(6)-amino-2-(p-aminophenyl)benzimidazole and terephthaloyl dichloride. An exemplary polyester is aromatic polyester available from Kuraray Co. Ltd. under the tradename VECTRAN. A suitable aliphatic polyamide is nylon such as PA66 available from Invista, Wilmington, Del. The aromatic polyamide polymer may be m-aramid, such as Nomex®, or p-aramid such as Kevlar®, both being available from E.I. DuPont de Nemours and Company, Wilmington, Del. (DuPont). A suitable polyazole is polyoxadiazole such as is available under the tradename Arselon from OJSC SvetlogorskKhimvolokno, Svetlogorsk, Belarus. An exemplary bio-based polymer is polytrimethylterephthalate (PTT) available from DuPont under the tradename SORONA. A suitable polyimide is Kapton® available from DuPont. A suitable polyamide-imide is Kermel® available from Kermel, Colmar, France. In one embodiment, the first yarn is m-aramid and the second yarn is p-aramid. Other exemplary preferred combinations of first and second yarns are listed in Table 1.

TABLE 1 First Yarn Polymer Second Yarn Polymer Polyester p-aramid Aliphatic polyamid p-aramid Polyoxadiazole p-aramid Polyamide-imide p-aramid

A hybrid cord comprising the first and second yarns may be used as is or formed into a woven or knit fabric. The term woven fabric includes a unidirectional fabric which is a fabric style in which the majority of yarns of the fabric are aligned parallel to each other. A fabric construction is particularly suitable for use in components that are subject to burst pressure testing at low temperatures such as room temperature and fatigue testing at high temperatures such as 175 degrees C. An example of such a component is a turbocharger hose where the cords provide structural reinforcement to an elastomeric material. Similar applications may be found in other mechanical rubber goods applications such as conveyor belts and tires.

A hybrid cord structure as described above will have an elongation at break greater than the elongation at break of the second yarn.

The hybrid cord may be produced in a single step on conventional ring spinning or twisting machines such as a Twistec Duo model TWV-250-1M equipped with a positive yarn feeder. FIG. 2 shows schematically how the cord may be produced. The hybrid cord axis is shown by the arrow X-Y.

The untwisted first reinforcement yarn 11 is unwound, in the hybrid cord axis direction, from a bobbin into the machine under a tension T1 and at a speed V1. Typically, T1 is in the range of from 100 N to 600 N and V1 in the range of from 5 to 100 m/min. The untwisted second reinforcement yarn 12 is unwound from a bobbin into the machine under a tension T2 and at a speed V2 in an angular direction, α, to the direction of the first yarn. The angle α is also referred to herein as a convergence angle. This angle is also sometimes known as a feed angle. The convergence angle α may be from 10 to 90 degrees, more preferably 10 to 50 degrees or even 10 to 30 degrees. Preferably T2 is close to zero but is never zero, with a typical range being from 1 to 50 N. T1 is always greater than T2 and V2 always greater than V1. A preferred range for V2 is from 5 to 100 m/min. In some embodiments, the difference between T1 and T2 is at least 50 g, or at least 100 g or even at least 200 g. In other embodiments the difference between T1 and T2 may be in the range 60-600 g.

The first and second yarns are fed to cylindrical feed rollers (15 and 16 in FIG. 6) and combined to meet at a convergence point in eyelet 13 so as to form hybrid cord 10. The first yarn passes through the nip between rollers 15 and 16 whereas the second yarn passes over the outer surface of roller 15 as shown in FIG. 6. The different yarn paths allow for a differential tension and line speed between the two yarns. The relative tensions and speeds of the first and second yarns going into the eyelet 13 is such that the second yarn bulks around the first yarn at the desired convergence angle. In some embodiments, the second yarn is a singles yarn and covers at least 80% or at least 85% or at least 90% or at least 95% or 100% of the surface area of the first yarn. Twist, either S or Z, is applied to the hybrid cord prior to winding onto a take-up bobbin. S twist is shown in FIG. 2 by arrow 14 with Z twist being in the opposite direction. The second yarn is wrapped around the first yarn at an angle of from 5 to 40 degrees. This angle is referred to herein as a wrap angle. More preferably, the wrap angle is 15 to 30 degrees or even 18 to 25 degrees.

As the hybrid cord has torque, an optional additional feature is to pass the cord through a steam chamber in order to stabilize (fix) the cord.

A cord as described above may be used as a reinforcement component of a hose such as a turbocharger hose. In some hose embodiments, there may be a plurality of layers comprising a cord as described above. Preferably the cord is formed into a fabric such as a woven or knit fabric which is subsequently combined with elastomers in the construction of the hose.

EXAMPLES

The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Examples prepared according to the process or processes of the current invention are indicated by numerical values. Control or Comparative Examples are indicated by letters.

In all four examples, the first yarn (11) was a Nomex® meta-aramid T 430 filament yarn having a linear density of 1330 dtex that was commercially available from E. I. duPont de Nemours and Company, Wilmington, Del., hereinafter (DuPont). This yarn had a tenacity of 5.5 g/dtex (4.98 g/denier), a modulus of 15.5 GPa (111 g/dtex) and an elongation at break of 30 percent. In all examples, the second yarn (12), a singles yarn, was Kevlar® T956 K29AP merge 1W065 para-aramid filament yarn having a linear density of 1670 dtex also from DuPont. This yarn had a tenacity of 30 g/dtex (27 g/denier), a modulus of 93 GPa (666 g/dtex) and an elongation at break of 3.9 percent.

In all four examples, the hybrid cord was prepared on a Twistec Duo two spindle twisting machine model TWV-250-1M equipped with a positive yarn feeder from TwisTechnology, Barcelona, Spain. FIGS. 3-6 show the machine configurations used for the different examples. The yarn tension was measured between nip point 17 and eyelet 13 using a conventional yarn tension measurement unit.

All spools of hybrid yarn were finished by placing them in a Welker 5772 autoclave and subjected to steam at a temperature of 120 degrees C. for three periods of 30 minutes. The pressure in the autoclave was 2 bar.

The lengths of the first and second yarns in the hybrid cords were determined by cutting a length of cord, unwinding the two component yarns to separate them and measuring their respective lengths. This is reported as “Overfeed %” in Table 2.

Comparative Example A

This was made according to FIG. 3. First and second untwisted yarns 11 and 12 were fed from their respective yarn spools through first and second eyelets 11 a and 12 a respectively. The two eyelets 11 a and 12 a were as close to each other as possible so that the two yarns merged at a convergence angle, α, that was as close to zero as practical at 0.5 degrees. In this example, eyelets 11 a and 12 a could be replaced by one large eyelet. The two yarns were then fed between nip rolls 15 and 16. The nip point of the rolls is shown by line 17. After passing through the nip rolls, the two yarns were fed through a further eyelet 13 where they merged to form a hybrid cord. The distance d₁ between the nip 17 and the third eyelet 13 was 206.3 mm. In the region of eyelet 13, the second yarn did not bulk, nor did it wrap around and cover the first yarn. The first and second yarns were merely twisted together at a wrap angle of about 12 degrees. The tension on both the first and second yarns was 450 g. The spindle speed was 4200 rpm/min and the line speed 21 m/min. After the hybrid yarn was formed at eyelet 13, it was then passed through a balloon ring 18 prior to being twisted as a Z twist at a level of 202 turns per meter and wound onto a spool. The second yarn was wrapped around the first yarn at an angle of about 12 degrees. In a hybrid cord made under these conditions, the second yarn was found to be only 0.2% longer than the first yarn.

Example 1

This was made under similar processing conditions to Comparative Example A except that the second yarn 12 was not fed through the nip but passed over the outer surface of nip roll 15 as shown in FIG. 4. The tension applied to the first yarn was 407 g and that on the second yarn was 40 g. The second yarn bulked and wrapped around the first yarn in the region of eyelet 13 to cover more than 70 percent of the surface area of the first yarn. The angle of convergence of the two yarns was 2.2 degrees. The hybrid yarn had a Z twist at a level of 199 turns per meter. The second yarn was wrapped around the first yarn at a wrap angle of 18.6 degrees. In a hybrid cord made under these conditions, the second yarn was found to be 6.3% longer than the first yarn.

Comparative Example B

The twisting machine was arranged as in FIG. 5. The difference between this arrangement and that of FIG. 3 was that the two eyelets 11 a and 12 a were separated by a distance d₂ of 55 mm. This in turn caused the second yarn 12 to merge with the first yarn 11 in eyelet 13. The distance d₁ was 206.3 mm. The tension on both the first and second yarns going into the nip was 450 g. The spindle speed was 4200 rpm/min and the line speed 21 m/min. In the region of eyelet 13, the second yarn did not bulk, nor did it wrap around and cover the first yarn. The first and second yarns were merely twisted together at a wrap angle of 12.4 degrees. The angle of convergence of the two yarns was 14.9 degrees. After the hybrid yarn was formed at eyelet 13, it was then passed through a balloon ring 18 prior to being twisted as a Z twist at a level of 202 turns per meter and wound onto a spool. The second yarn was wrapped around the first yarn at an angle of about 12 degrees. In a hybrid cord made under these conditions, the second yarn was found to be only 0.2% longer than the first yarn.

Example 2

This was made under similar processing conditions to Comparative Example B except that the second yarn 12 was not fed through the nip but passed over the outer surface of nip roll 15 as shown in FIG. 6. The tension applied to the first yarn was 510 g and that on the second yarn was 10 g. The second yarn bulked and wrapped around the first yarn in the region of eyelet 13. The second yarn covered more than 90 percent of the surface area of the first yarn. The angle of convergence of the two yarns was 15.2 degrees. The hybrid yarn had a Z twist at a level of 203 turns per meter. The second yarn was wrapped around the first yarn at a wrap angle of 24.6 degrees. In a hybrid cord made under these conditions, the second yarn was found to be 7.7% longer than the first yarn.

A summary of some hybrid cord forming features is presented below in Table 2.

TABLE 2 Overfeed Component % of 2^(nd) Yarn Cord Wrap Yarn to Example Feed Angle (°) Angle (°) 1st Yarn Comments Comparative A 0.5 11.6 0.2 Second yarn did not wrap around first yarn Example 1 2.2 18.6 6.3 Second yarn covered 70% of first yarn Comparative B 14.9 12.4 0.2 Second yarn did not wrap around first yarn Example 2 15.2 24.6 7.7 Second yarn covered 90% of first yarn

Mechanical Strength of Hybrid Cords

The cords produced in the above examples were evaluated for strength as strands and as loops. Breaking strength (maximum force to break) and percentage elongation at break were determined according to test methods ASTM 7269 issue 07 and ASTM 3217 issue 07 respectively. The data is summarized in Table 3. The linear density of all the cords was measured to be 3002 dtex according to test method ASTM D1907 issue 07. The tabulated results are the mean values of 15 samples for each example.

TABLE 3 Strand Force Strand Loop Force Loop to Break Elongation at to Break Elongation Example Fmax (N) break (%) Fmax (N) at break (%) A 256.9 5.11 288.3 3.5 1 211.4 5.59 266.7 4.08 C 256.5 5.01 308.3 3.66 2 214.7 6.7 239.6 5.51

The results demonstrate the superior elongation at break of the cord of Examples 1 and 2. The force to break value of Example 2 is deemed to be acceptable.

FIG. 7 is a force vs. strain curve for the examples when tested as strands. FIG. 8 is a force vs. strain curve for the examples when tested as loops. Both these figures show benefits in mechanical performance for Examples 1 and 2 when compared with the comparative examples. 

What is claimed is:
 1. A hybrid cord comprising (i) a first yarn, without initial S or Z twist, of continuous polymeric filaments forming the core of the cord, the yarn having a tenacity of 2.2-16.6 g/dtex, a modulus of from 1 to 20 GPa and an elongation at break of greater than 8%, the yarn being a non-bulked yarn, (ii) a second yarn, without initial S or Z twist, of continuous polymeric filaments, the yarn having a tenacity of greater than 16.6 g/dtex, a modulus of greater than 20 GPa and an elongation at break of no greater than 8%, the second yarn being a bulked yarn that is wrapped around the first yarn, wherein, (a) the second yarn is wrapped around the first yarn at an angle of from 5 to 40 degrees, (b) the second yarn has a length that is from 4 to 35 percent longer than that of the first yarn, and (c) the hybrid cord is unbalanced and has an S or Z twist.
 2. The cord of claim 1, wherein the polymer of the first or second yarns is polyester, aliphatic polyamide, aromatic polyamide, aromatic co-polyamide, aromatic copolymer, polyazole, polyimide, polyamide-imid or a bio-based polymer.
 3. The cord of claim 1, wherein the second yarn has a length that is from 6 to 15 percent longer than that of the first yarn.
 4. The cord of claim 2, wherein the aromatic polyamide is m-aramid or p-aramid.
 5. The cord of claim 2 wherein the polyazole is polyoxadiazole.
 6. The cord of claim 2, wherein the aromatic copolymer is a copolymer of para-phenylenediamine, 5(6)-amino-2-(p-aminophenyl)benzimidazole and terephthaloyl dichloride.
 7. The cord of claim 3, wherein the second yarn has a length that is from 4 to 10 percent longer than that of the first yarn.
 8. The cord of claim 4 wherein the first yarn is m-aramid and the second yarn is p-aramid.
 9. A turbocharger hose comprising the cord of claim 1 as a reinforcement material. 